The big question is, is that enough? The new iPad isn't cheaper, and there are no barnstorming new features - so for example the TouchID fingerprint scanner hasn't made its way across from the iPhone 5S - and of course rivals are catching up.

Is the iPad Air good enough to stay ahead of the competition? Here are the key differences between the new iPad Air and the outgoing iPad 4.

1. The iPad Air is really, really thin

The move to retina displays made the previous iPad considerably more porky than its predecessor, but the iPad Air has been on the Atkins diet: it's 20 percent thinner at just 7.5mm.

That's a whopping 2.2mm thinner than the outgoing iPad 4 and more than a millimeter thinner than Google's Nexus 10 or Nokia's 2520, and it makes a surprising difference to the way the iPad Air looks.

2. The iPad Air is really, really light

Apple hasn't just given the fifth generation iPad a really good squeeze. It's made serious weight savings too. The iPad Air weight is just one pound, or 469g in real money. The iPad 4 is 635g, which makes it tiring to hold for long periods.

This new iPad should be considerably more comfortable for longer. That's particularly important if you tend to do a lot of reading on your iPad - on the iPad 4 even short stories end up giving you gorilla arms - and of course it means it won't be as heavy to lug around either, which was a major drawback of the iPad 4.

3. The iPad Air is an awful lot smaller

The bezel's 43% smaller than before, and that reduction slims the iPad Air from a previous width of 185.7mm to a more slender 169.5mm. It's lost a millimeter of height too, although that change isn't exactly noticeable.

The thinner sides do make a difference, though: while the screen remains unchanged the useless area around it is significantly slimmer, once again making the device more portable and more comfortable to hold for long periods.

4. The iPad Air has got a processor that goes wheeeeeeeee

As widely predicted, the iPad Air gets Apple's most powerful mobile processor, the A7, which runs eight times faster than the original iPad.

It's a 64-bit processor that promises to do everything twice as well, so graphics performance is two times better, performance is two times faster, twerking videos are two times twerkier and so on.

It isn't two times greedier, though: Apple promises that you'll get the same ten-hour battery life of its other iPads. The iPad Air also gets the M7 motion sensing chip from the iPhone 5S.

5. The iPad Air has much better Wi-Fi

It doesn't get the ultra-fast 802.11ac Wi-Fi that Apple's rolling out in its laptops, but the radio in the iPad Air is still much better than before: it's the first iPad to get MIMO (multiple input, multiple output) multiple antennas for its 802.11n Wi-Fi, which means it's capable of up to 300Mbps downloads.

It can also connect to slower 802.11a/b/g networks, and it supports both 2.4GHz and 5GHz frequency bands.

7. The iPad Air is packed with free apps

The apps are all brand new versions, although Garageband isn't entirely free: some instruments and sounds will require in-app purchases.

They've also been developed in conjunction with the new OS X versions, so you'll be able to share documents between desktop and iPad apps via iCloud - something that hasn't exactly been great in previous versions.

There's a catch, though: sharing documents from iWork with the Mac requires the latest versions of the desktop iWork apps, which are only available for OS X Mavericks.